Klima-indusert hygrotermisk ytelse av en stål-tre forbindelse i Tretten bru og dens innvirkning på den konstruksjonstekniske oppførselen.

Abstract

The primary objective of this master’s thesis is to conduct an analysis of the climate-induced hygrothermal stresses in dowel-type joints within glulam truss bridges. Both wood and steel, the primary materials used in these joints, are sensitive to climatic changes. Given that structures like glulam truss bridges are exposed to diverse environmental conditions, it is crucial to examine how these fluctuations may influence their long-term structural performance. The study employs numerical analysis to examine four sections of the joint structure from the case study, facilitating exploration of consistent climatic factors across varying sections. Uniform environmental conditions ensure methodological rigor and enable meaningful comparative analysis. The analysis progresses through hygrothermal analysis using WUFI® 2D, computational processing of output (in Excel) for ABAQUS, and structural analysis within ABAQUS.

The findings indicate that moisture content variations have minimal effect on steel performance across the entirety of the joint, while significantly impacting wood. The outermost wood sections demonstrate the largest fluctuations in moisture content, with the exception of the upward-facing side shielded by a metal cover. The presence of dowel holes accelerates moisture penetration, leading to rapid increases in moisture levels compared to other areas. However, moisture content stabilizes progressively towards the joint’s core due to the presence of continuous steel plates and dowels acting as barriers.

Thermal energy infiltrate the joint’s core with minimal dissipation for both steel and wood. Steel exhibits larger deformations in response to temperature variations compared to wood. Despite wood’s more pronounced deformations in the exposed part of the joint, steel displays greater deformations in segments further into the joint. Notably, steel often bears maximum stresses in both the exposed part and the core due to its higher load-carrying capacity. However, the thesis reveals that within the wood, the maximum hygrothermal stresses occur in the exposed part where it meets the first steel plates—coinciding with the area prone to block tear-out, the likely cause of the collapse of the Tretten bridge. While this simulation did not demonstrate a significant reduction in capacity, it does not preclude the possibility of its contribution to the block tear-out.

Keywords: hygrothermal analysis; steel-wood connections; structural analysis; climate-induced effects; structural integrity; thermal stress; Moisture induced stress; Finite element model- ling